Lateral marks: red, green, can and cone.

What does a lateral mark tell you?

Which side of a channel you are looking at, measured against the conventional direction of buoyage. In Region A, red marks the port side and green the starboard side. In Region B the colours are reversed: red to starboard, green to port.

The direction of buoyage is either the general direction you take approaching a harbour, river, estuary or other waterway from seaward, or a direction set by the competent authority. It must be shown on the charts and nautical documents.

Which side do I keep a port-hand mark on?

On your port side when you are heading in the direction of buoyage — for example, inbound from seaward where that is the direction of buoyage. In practice, heading the other way you keep it on your starboard side: the mark has not changed, your heading has.

If the marks are numbered, the numbers run in the direction of buoyage, with even numbers on red marks and odd numbers on green — R1001's protocol, especially in confined waterways.

What shapes are lateral marks?

Port-hand marks are cylindrical (can), pillar or spar. Starboard-hand marks are conical, pillar or spar. That holds in both regions — only the colours swap.

A pillar or spar doesn't show which side it marks by its shape, so R1001 says a lateral mark that doesn't rely on shape should carry the matching topmark where practicable: a single can for port-hand marks, a single cone, point upward, for starboard-hand marks. Where weather or ice make topmarks impractical, the authority may decide not to use them.

What light does a lateral mark show?

If one is fitted, a light of the mark's own colour — red on a red mark, green on a green one — with any rhythm except composite group flashing (2 + 1), which is reserved for preferred channel marks. A lateral mark may also carry an AIS AtoN or a racon.

What does a port-hand mark look like?

A can, pillar or spar buoy, with a single can in the mark's colour as its topmark if it carries one. In Region A it is red, with a red light if lit; in Region B it is green, with a green light. The light may have any rhythm except composite group flashing (2 + 1).

What does a starboard-hand mark look like?

A conical, pillar or spar buoy, with a single cone, point upward, in the mark's colour as its topmark if it carries one. In Region A it is green, with a green light if lit; in Region B it is red, with a red light. The light may have any rhythm except composite group flashing (2 + 1).

So in Region B a red cone is a starboard-hand mark and a green can is a port-hand mark. The can is always port and the cone always starboard; only the paint and the light change.

What is a preferred channel mark?

Where a channel divides, a modified port or starboard lateral mark can show which branch is the preferred channel — 'the primary route or channel' designated by the competent authority — for a vessel proceeding in the direction of buoyage. It carries one broad horizontal band of the other lateral colour, and its light, if fitted, is composite group flashing (2 + 1) in the mark's main colour.

What do preferred channel marks look like?

Preferred channel to starboard: a port-hand mark (can, pillar or spar, with a can topmark) in the port-hand colour, with one broad horizontal band of the starboard-hand colour. In Region A that is red with a green band and a red light; in Region B, green with a red band and a green light. If lit: composite group flashing (2 + 1).

Preferred channel to port: a starboard-hand mark (conical, pillar or spar, with a cone topmark, point upward) in the starboard-hand colour, with one broad horizontal band of the port-hand colour. In Region A that is green with a red band and a green light; in Region B, red with a green band and a red light. If lit: composite group flashing (2 + 1).

Which side do I pass a preferred channel mark?

As we read R1001's tables, a preferred-channel-to-starboard mark is a modified port-hand mark (it has the port-hand shape and topmark), so proceeding in the direction of buoyage and following the preferred channel you keep it on your port side, as you would any port-hand mark, and the preferred channel lies to starboard of it. The preferred-channel-to-port mark is the mirror image: a modified starboard-hand mark, kept on your starboard side.

A memory aid of ours: to follow the preferred channel, read the mark by its main colour, shape and topmark, as if the band weren't there. That tells you which side to keep it. The band adds that the channel divides here. If you are taking the other branch, keep the mark on the opposite side.

What might they ask about lateral marks?

Examples of the kind of question to be ready for (our wording, not the MCA's):

“You are entering harbour in Region B and see a red conical buoy ahead. Which side do you keep it on?”

“What would a preferred-channel-to-port mark look like in Region A, by day and at night?”

“Which light rhythm can an ordinary lateral mark not use, and why?”

“You are leaving harbour in Region A. Which side do you keep the green marks on?”

The common slips: assuming red always means port, forgetting that 'port hand' is measured in the direction of buoyage rather than your own heading, and naming a preferred channel mark by its band colour instead of its main colour.

Can lateral marks mark a new danger?

Yes. R1001 lists lateral marks among those that can mark a newly discovered danger. If a lighted lateral mark is used as a duplicate mark on a new danger, it must show a very quick (VQ) or quick (Q) light — see the emergency wreck mark page for how new dangers are marked.